That comment was in reference to the fact that you can't bring an offline character online. So if you want to play offline and then want to play online with friends using that character, there is no possible way for that to be accommodated. Forcing online means that people can always play with each other on any character
There are many reasons to play offline online, although the comment wasn't in reference to that. For example, being a mouseclick away from arguing with stubborn people on internet forums is one of many such benefits.